Recently, optical information recording systems capable of stably recording a large amount of information at a very high recording density have as optical disks, compact disks or external recording equipments for computers.
An objective lens is an essential component of such an optical recording system to focus a light beam in a spot of light on the information recording surface of an optical information recording medium to read or write information. An objective lens driving device for the positional control of the objective lens plays a very important role in correcting the tracking error and the focusing error of the spot of light.
FIG. 1 is an exploded perspective view of a conventional objective lens driving device.
The objective lens driving device shown in FIG. 1 includes armature holder 1 and a base yoke 2.
The upper portion of the armature holder 1 is formed in the shape of an oblate hexagon or a rhombus having one end fixedly provided with an objective lens 3 and the other end fixedly provided with a counterweight 4 for counter-balancing the objective lens 3. A focus control coil 5 and track control coils 6a, 6b, . . . are disposed in a cylindrical arrangement on the bottom center of the armature holder 1.
The objective lens 3 and the counterweight 4 thus mounted on the armature holder 1 are fitted respectively in openings 7a and 7b formed near the opposite sides of a substantially square supporting rubber member 7. The supporting rubber member 7 is fastened to a stator base 9 with screws 8a and 8b.
The stator base 9 is provided with a central opening 9a. The control coils 5 and 6 disposed on the armature holder 1 project downward through the opening 9a. A cover 10 is attached to the upper surface of the stator base 9.
The base yoke 2 includes a holding yoke 13 for holding permanent magnets 11a and 11b and a support shaft 12, and yokes 14a and 14b attached to the upper surfaces of the permanent magnets 11a and 11b, respectively.
The armature holder 1 is mounted on the support shaft 12 so as to be axially slidable and rotatable relative to the base yoke 2.
FIG. 2 is a longitudinal sectional view of the assembly of the armature holder 1 and the base yoke 2, in which the parts corresponding to those shown in FIG. 1 are denoted by the same reference numerals and the description thereof will be omitted.
As is obvious from FIG. 2, a coil holder 15 is disposed on the bottom surface of the armature holder 1. The focus control coil 5 and the track control coils 6 are fixed to the coil holder 15.
The armature holder 1 is provided on the bottom thereof with a cylindrical bearing 16, which receives the support shaft 12 therein.
The control coils 5 and 6 are fixed to the armature holder 1 as shown in FIG. 3.
The focus control coil 5 is attached to the coil holder provided on the bottom of the armature holder 1, and the track control coils 6a, 6b, 6c and 6d are fixed to the focus control coil 5. Leads 17a, 17b, . . . and 17j lead out from the coils.
Motions of the conventional objective lens driving device will be described hereinafter. A light beam, such as a laser beam, is emitted through the objective lens 3 so as to be focused in a spot of light on an optical information recording medium, such as an optical disk. When the light beam is out of focus, the objective lens 3 can be focused by supplying a control current corresponding to a focal displacement to the focus control coil 5 to slide the armature holder 1 in either of the directions indicated by a double-head arrow A due to the interaction between the control current and the permanent magnets 11. Although the armature holder 1 is joined through the objective lens 3 and the counterweight 4 to the supporting rubber member 7, the objective lens 1 is slidable because the supporting rubber member 7 is bendable.
When the spot of light deviates from a track, the track control movement of the objective lens 3 can be achieved by supplying a control current corresponding to the deviation of the spot of light from the track to the track control coils 6a, 6b, . . . and 6d to turn the armature holder 1 in either of the directions indicated by a double-head arrow B due to the interaction between the control current and the permanent magnets 11.
The conventional objective lens driving device thus constructed has a problem that it is difficult to manufacture the objective lens driving device.
That is, the leads 17a, 17b, . . . and 17j of the focus control coil 5 and the track control coils 6a, 6b, . . . and 6d included in the armature unit of the objective lens driving device must be connected to the stator unit, which requires difficult wiring work. Moreover, because the armature unit and the stator unit are interconnected by the supporting rubber member 7 to set the center of a range of track control movement in which the armature unit of the objective lens driving device can be moved for track control, it is difficult to assemble the armature unit and the stator unit.
Furthermore, the lead wiring work and the attachment of the supporting rubber must be carried out strictly, or troubles occur in the control actions of the objective lens driving device.